The overall objective of this proposal is to develop basic research skills in immunology and biochemistry through the investigation of mast cell membrane glycosphingolipids. The proposed research is designed to learn more about mast cell differentiation through studies of the expression and function of a cholera toxin-binding glycosphingolipid, ganglisoside GM1, on mouse mast cells at different stages of development. The binding of cholera toxin to ganglioside GM1 on the plasma membranes of interleukin 3- dependent, mouse bone marrow culture-derived mast cells induces an increase in both the histamine content and the DNA synthesis of these cells. The first specific aim is to quantify the surface expression and biosynthesis of ganglioside GM1 in culture-derived mast cells maintained in interleukin 3 with or without an additional proliferative signal from interleukin 4, in culture- derived mast cells further differentiated in vitro by co-culture with fibroblasts, and in peritoneal mast cells ex vivo; and to determine if the effects of cholera toxin on the histamine and cyclic adenosine monophosphate contents of these populations correlate with ganglioside GM1 expression. The second specific aim is to determine whether cholera toxin increases the histamine content of culture-derived mast cells by augmenting their histidine uptake and/or decarboxylation of histidine, and if so, to determine whether this effect correlates with ganglioside GM1 expression in the more differentiated mast cell populations. The third specific aim is to determine whether cholera toxin promotes DNA synthesis in the mast cell populations by acting as a cell cycle progression factor and whether the effect of the toxin is similar or different than that of interleukin 4. The proposed research will yield new basic information about the first glycosphingolipid-dependent functional response to be described in mast cells. These responses involve two important aspects of mast cell biology, namely, control of cellular histamine content and the regulation of mast cell replication. While these studies will focus on mouse mast cells, the knowledge and skills obtained should be directly applicable to future studies of the immunobiology and biochemistry of human mast cells, including those involved in ocular immediate hypersensitivity reactions.